Controlling hydrogen partial pressure in a reforming process



Aug.. 2 1966 w. Q. WWF-'Ema 3,264,207

CONTROLLING HYDROGENPARTIL PRESSURE IN REFORMING PROCESS Filed Sept. 8, 1961 MZOM ZOrPdJJfPwE\ @www Vilm

United States Patent O 3 264 207 CONTROLLING HYDROGEN PARTIAL PRESSURE IN A REFORMING PROCESS William C. Pfelierle, Middletown, NJ., assigner, by mesne assignments, to Sinclair Research, Inc., New York,

N.Y., a corporation of Delaware Filed Sept. 8, 1961, Ser. No. 136,950 6 Claims. (Cl. 208-65) Thls lnvention is a continuation-in-part of my copending application Seria-l No. 125,994, led July 24, 1961, now abandoned. The present invention pertains to the catalytic reforming of petroleum naphtha. More specifically the present invention relates to a new and improved method of operating a multiple bed catalytic reforming system. Particularly the instant invention provides a method of realizing substantially all of the benets obtained in low pressure reforming in such a system while maintaining a relatively high pressure;

In the reforming of hydrocarbons, particularly straight run naphtha fractions, using for instance a platinum group metal-alumina catalyst, various reactions occur, such as isomerization, dehydrocyclization, dehydrogenation, and hydrocracking, all of which lead to hydrocarbon products of increased octane ratings usually greater than about 80 to 85 RON (neat). After a period of use in such a system, however, the catalyst becomes gradually deactivated due to the deposition of coke particles on the surface of the catalyst and consequently a decrease in the octane values of the -reformate product is observed. If the octane requirements imposed upon the particular system are to be continuously met, the catalyst must 'therefore be restored in activity with this usually being accomplished by various regeneration techniques involving the burning of carbon lfrom the catalyst by contact with an oxygen-containing gas.

The reforming process is conventionally carried out under conditions including contacting the feedstock, `for instance a straight run naphtha, with a reforming catalyst at about 875 to 975 F. and at about 250 to 500 p.s.i.g. pressure at a weight hourly space velocity (WHSV) Within the range of about 0.5 to land a hydrogen recycle ratio of about 4:1 to 12:1 moles based on the moles of naphtha feed. The catalyst employed can be a -supported platinum catalyst containing for instance about 0.1 to 1.5 percent by weight platinum, preferably from about 0.3 to 1.0 percent and the support can be alumina characterized for instance by high surface area and large pore size. Stich catalysts can be conveniently prepared as described in U.S. Patents Nos. 2,838,444 and 2,838,- 445. When employing these reforming operations `a plurality of adiabatic catalyst beds are usually provided, for instance 3, 4, 5 or more in number, and the hydrocarbon feed can be preheated to the desired inlet temperature before entry into each succeeding catalyst bed. In a multiple bed essentially adiabatic reaction system, a plurality of fixed beds containing the reforming catalyst can be arranged for serial iiow of the feedstock and in such a manner that the beds can be removed from the processing cycle, usually one at a time, and the catalyst regenerated without a break in the continuity of operation. Subsequently the regenerated bed can be placed on stream with another bed being removed to undergo regeneration in like manner. This procedure is particularly applicable to catalyst beds or reactors subsequent in line to the initial reactor, preferably the terminal reactor, in order to extend the length of the processing cycle since the catalyst in a subsequent reactor is more quickly deactivated than that in the preceding reactor. This deactivation is due to the maintenance of a higher average temperature in the subsequent reactor catalyst bed.

As a result the catalyst in each Isucceeding reactor will become partially deactivated in less time than the catalyst of the preceding reactor and in order to insure a vhigh grade reformate the catalyst in the reactors is periodically regenerated. This can be accomplished in a multiple bed system by, for instance, 'blocking out a reactor, which may be a so-called swing reactor, while the remaining reactors are continued in their normal processing cycle. The blocked out reactor, in order to regenerate the catalyst contained therein, can be depressured and purged with an inert gas. After purging, a flow of free oxygencontaining regeneration gas is established, and regeneration initiated. The reeneration can be conducted at a temperature in the range of about 700 to 950 F. with the final stage being conducted at about 850 to 950 F. When the activity of the catalyst has been restored, i.e., when the predominant portion of the carbon Vdeposits is burned off, the oxygen flow is stopped and the inert gas flow started. The system can then be depressured and evacuated several times in order :to insure complete oxygen rem-oval. Prior to placing the reactor on stream again, it is pressured with a hydrogen-containing gas from the recycle system and when operating pressures have been attained the block valves are opened, placing the unit in the reforming cycle. Subsequently, another reactor -can be treated in substantially the same manner. p The current trend in the operation of reforming units is to increase the severity levels for the production of reformates with clear octanes of about RON or higher. Reforming of highly paraiiinic charge stocks, such as those containing at least `about 50% by volume of paraiiins, to produce clear octanes of 100 RON requires severity levels even higher than those required to reform low parain content charge stocks. High severity reforming conditions include temperatures of about 900 to 990 F. and pressures yof about 100 to 400 p.s.i.g. Lower pressures are employed in high severity reforming primarily because dehydrocyclization of paraiiins to aromatics increases with decreasing pressure and yield advantages often outweigh other factors.4 Low pressure operation is disadvantageous, however, since catalyst deactivation is much more rapid and frequent regeneration is therefore required, and also due to the required increase in size or capacity of the equipment associated with the reactors in the reforming system, such as the recycle lines and recycle gas compressors, which would have to be installed in modifying` an existing unit or building a new one.

My copending application Serial No. 125,994 describes a processing sequence wherein the advantages of low pressure operation in terms of higher yields of high clear octane number product are obtained at high pressures, particularly when reforming a highly paraflinic charge stock containing at least about 50% by volume of paraffins.

The application is based on the finding that when operating a reforming reaction system at relatively high pressures but with a hydrogen partial pressure corresponding generally to that of a conventional low pressure operation, the balance of the pressuring gases being essentially a mixture of C1 to C3 alkanes, the yield-octane relationship is comparable if not improved, the reformate lead susceptibilities are improved, catalyst deactivation is less rapid and there is an increased net hydrogen make over conventional low pressure operation. These and other advantages are accomplished by carrying out the reforming processing operation under high severity conditions otherwise conventional but at a total pressure of about 300 to 1000 p.s.i.g., the gas introduced into the reforming reaction system other than hydrocarbon charge stock consisting essentially of hydrogen and at least one C1 to C3 alkane and the mole percent hydrogen in the gas so introduced multiplied by the total pressure of the gas so introduced being maintained on the hydrogen-rich side of the methane decomposition equilibrium but at least about 1% less than the partial pressure of the hydrogen in the hydrogen-containing recycle fraction of the efiiuent from the reaction system. Advantageously the hydrogen partial pressure in the hydrogen-containing recycle gas stream is maintained within the range of about 100 to 350 p.s..g. with a hydrocarbon partial pressure in the recycle gas stream higher than at least about 40% of the hydrogen partial pressure.

One of the methods disclosed in Serial No. 125,994 for adjusting the hydrogen content of the recycle gas stream is by separating from the reforming reaction effluent a fraction consisting essentially of hydrogen and at least one C1 to C3 alkane, separating substantially pure hydrogen from at least a portion of the so-separated fraction, and recycling the fraction so enriched in alkane content to the reforming reaction system. The latter separation can be accomplished, for example, by passing the fraction consisting essentially of hydrogen and at least one C1 to C3 alkane into a palladium type diffuser. Such a diffuser can comprise a bank of jacketed palladium or palladium alloy tubes connected in parallel and heated to a temperature of about 750 F. Substantially pure hydrogen passes through the palladium tubes into the jacketed section and is withdrawn, so that by this method it is possible to produce essentially pure hydrogen.

TheA present invention resides in the application and extension of the findings of Serial No. 125,994 to reforming of light hydrocarbon stocks containing a substantial Volume of paranic and naphthenic hydrocarbons in a reforming reaction system including successive serially connected reaction zones.

In reforming a conventional light hydrocarbon charge stock containing substantial quantities of paramns and naphthenes in a multiple bed essentially adiabatic reaction system, the rate of aromatics formation by dehydrogenation of naphthenes is more rapid than the rate of aromatics formation by dehydrocyclization of parains so that the eiiluent from the first reactor in the system seldom contains more than to 20% by volume of naphthenes even when the light hydrocarbon charge stock introduced into the first reactor contains up to about 60% by volume of naphthenes. Moreover, the predominant reaction in the first one or two reactors in the system, due primarily to the lower catalyst bed temperatures, is dehydrogenation of naphthenes to aromatics with a concomitant substantially large net hydrogen production, depending upon the volume percent of naphthenes in the naphtha hydrocarbon charge stock. Even with low naphthene content charge stocks, the increased extent of dehydrocyclization of parafiins to aromatics, when operating in accordance with this invention, produces sufficient hydrogen to more than offset hydrogen consumption due to hydrocracking, so that the net hydrogen produced by the reforming reaction system is at least 250 standard cubic feet of hydrogen per barrel of charge stock.

In accordance with the present invention, the reforming reaction system can be operated in a variety of ways to provide low hydrogen partial pressures in all or a selected number of the reaction zones in a multiple bed catalytic reforming system, including adding to the reforming reaction system a gas 'fraction enriched in C1 to C3 alkane, withdrawing from the reforming reaction system a gas fraction enriched in hydrogen, or by a combination of such steps, and for illustrative purposes, reference will be made to the accompanying drawing, FIG- URE 1 of which represents in schematic form a reforming reaction system and wherein FIGURE 2 represents a palladium diffuser comprising a bank of jacketed palladium or palladium alloy tubes connected in parallel and heated to a temperature of about 750 F. In FIGURE l, numeral 1 designates a feed line by way of which a preheated naphtha boiling in the range of about 150 to 400 F. is introduced into gas-fired preheater 2. The naphtha is heated to a suitable inlet temperature, i.e., about 915 F., and then is passed by way of line 3 to reforming reactor 4 containing a bed of a platinum on alumina type catalyst. Effluent from reactor 4 is passed to reheater 6 by way of line 5, wherein it is heated to a temperature of about 920 F., and .then to reactor 8 by way of line 7. Effluent from reactor is passed to reheater 10 by way of line 9, wherein it is heated to a temperature of about 925 F., and then to reactor 12 by way of line 11. Effluent from reactor 12 is passed by way of line 13 to reheater 14, wherein it is heated to a temperature of about 925 F., and then to reactor 16 by way of line 15. Effluent from reactor 16 is passed by way of line 17 to separator 18 from which gaseous products consisting essentially of hydrogen and C1 to C3 alkanes are withdrawn by way o'f line 19. Liquid product is withdrawn from separator 18 by way of line 20 and passed to distillation zone 21 which is shown as a single distillation tower but can be associated with a depropanizer or a debutanizer or both. Dissolved C1 to C3 alkanes are withdrawn from distillation Zone 21 by way of line 22, dissolved C4 alkanes are withdrawn by way of line 23 and C5+ reformate is withdrawn by way of line 24. Hydrogen containing gas withdrawn from separator 18 by way of line 19 is recycled to reactor 1by way of lines 25 and 3, make gas being removed by line 26, and start-up hydrogen being supplied by line 27.

FIGURE 2 shows a palladium diffuser 35 in schematic form and the dash lines in FIGURE 1 indicate the points at which the diffuser can be placed in the reforming reaction system shown in FIGURE 1. Also, dash lines 2S, 29, 30 and 31 indicate the points at which Cl to C3 alkanes can be introduced into the reforming reaction system shown in FIGURE 1.

The data presented in copending application Serial No. 125,944 and subsequently herein show that low hydrogen partial pressure operation is especially advantageous for highly parafiinic charge stocks. Thus, where the charge stock is derived from a Middle East crude and has a parafitin content of the order of 65-75 volume percent and a naphthene content of the order of 15-22 volume percent, then a relatively small capacity palladium diffuser can be installed in recycle gas line 25. Such an installation would require reheating of the recycle gas so that depending upon the amount of feed charged to the unit, economics may dictate placing the palladium diffuser in `line 17. Where the charge stock is of intermediate naphthene content, i.e., 25-35 volume percent, the diffuser is with advantage placed in line 7 after the Ifirst reactor and reheater since at this point in the reforming reaction system hydrogen production is substantially large and removal of a substantial amount of this hydrogen make promotes paraiin dehydrocyclization in the subsequent reactors under conditions of low hydrogen partial pressure. With higher naphthene content feeds, the diffuser is with advantage placed in line 11 after the second reactor and reheater since naphthene dehydrogenation is substantially complete at this point in the system. With low paraffin, high naphthene content charge stocks, and where the octane number requirement imposed upon the reforming reaction system is of the order or to 100 or more, the dif- 'fuser can with advantage be placed in line 15 after the third reactor and reheater. The amount of hydrogen withdrawn from the system by means of one or more paliladium type diffusers, wherever placed, is `at least 250 standard cubic feet of hydrogen per barrel of charge stock and can range up to the total net hydrogen make of the reforming reaction system. Since the reforming reaction system also produces a net C1 to C3 alkane make, withdrawal of hydrogen from any point in the system Will result in a reduced hydrogen partial pressure for the recycle gas stream.

In like manner, C1 to C3 alkanes can be introduced into the reforming reaction system by means of any of lines 28, 29, 30 and 31 to adjust the hydrogen partial pressure in the reforming reaction system, or a combination of C1 to C3 alkane introduction and hydrogen withdrawal can be employed.

If a diffusion unit is used such that a small amount of hydrogen is withdrawn relative to the units diffusion capacity, then the hydrogen on the effluent `(pure hydrogen) side of the diffusion unit Will be essentially in equilibrium with the hydrogen in the gas stream passing through the diifuser. Thus a diffusion unit can be used to measure the partial pressure of the hydrogen in the recycle or processing gas stream. Other means, such as the use of a hydrogen analyzer, may also be used to measure the partial pressure of the hydrogen in these streams. lIn response to this measurement, 'varying the rate of hydrogen withdrawal from the reformer permits control of the partial pressure of the hydrogen in the gas stream. These convenient means of controlling hydrogen content and hydrogen partial pressure in the recycle or processing gas streams provide an additional operating variable affecting product yield and octane as well as catalyst life.

Alternatively, hydrogen can be separated from the recycle fraction consisting essentially of hydrogen and at least one C1 to C3 alkane by other means known to the art as by preferential absorption of the alkane in a liquid hydrocarbon in an absorption-desorption system or by low temperature fractionation.

In addition, operation of the reforming reaction system with a high C1 to C3 alkane content recycle gas stream together with a high recycle ratio of about 20 moles of hydrogen per mole of feed :or higher permits the use lof fewer reactors and/ or reheatcrs in the reaction system due to the increased heat capacity of the recycle gas stream.

' The high severity reaction conditions employed are those which produce a reformate having an octane number clear of at least about 90 or preferably at least about 100 RON or more and generally fall Within the following ranges: temperature, about 875 1F. to 990 F., preferably at least about 920 F.; pressures, about 300 to 1000 p.s.i.g., prefer-ably about 300 to 500 p.s.i.g.; recycle gas ratios orf about `3 to 50 moles of hydrogen per mole of hydrocarbon feed; and space velocity, about 1 to 20 WHSV. The catalysts employed are the platinum group metal reforming catalysts. Generally these comprise about 0.1 to 2.0% by weight of a platinum group metal component on an alumina base. Such catalysts can include promoters. The platinum group metal of the catalyst is the essential component and these metals include for instance platinum, rhodium, palladium and iridium.

The feeds employed are the conventional petroleum reforming stocks boiling in the naphtha range, i.e. about 140 to 400 F., which contain about 20 to 95 volume percent of parains, Yprefer-ably about 40 to 75 volume percent of paraiiins, since the advantages of the invention are more significant the higher the proportion of paratins in the charge stock. The proportion of naphthenes in the charge stock is not critical and can range up to about 60% by volume. Typical of these high paraflin content charge stocks are those whose inspections are set out below:

6 Also, the charge stock most advantageously is substantially 'free from water and materials which would produce water in the reaction zone so that the water and sulfur content of the total yfeed including recycle gas and hydrocarbon charge stock entering the reaction system at all times during hydrocarbon charge stock introduction to the system are maintained below about 150 parts of water per million parts by volume of total feed in vapor phase and 25 parts of sulfur per million parts by weight of total feed, and the Water and sulfur content of the efuent withdrawn from the reforming reaction system at all times during hydrocarbon charge stock introduction to the system are maintained below about 100 parts of water per million parts by volume of total eiiiuent in vapor phase and 25 parts of sulfur per million parts by weight of total etiiuent.

The advantages of reforming in accordance with the present invention are most pronounced when the catalyst has not been damaged by simultaneous contact of water and a hydrocarbon containing gas with a Virgin or freshly regenerated catalyst at high temperatures of the order of 850 to 1100 F. and higher prior to or during a processing cycle as is described in my copending `application Serial No. 125,992, [filed July 24, 19611. Thus as described in that application, the virgin or freshly regenerated catalyst is preferably reduced using hydrocarbon free hydrogen and if a hydrogen containing gas also containing hydrocarbons is employed to reduce the catalyst, then the water content of the effluent withdrawn from the reforming reaction system at all times during catalyst reduction is maintained lbelow about 100 parts of water per million parts by volume of total eiiluent in vapor phase.

The operation of a multiple bed reforming reaction system employing a charge stock containing a substantial 'volume percent of both parafinic and naphthenic hydrocarbonsis most advantageously carried out in accordance with this invention by employing a relatively low recycle ratio inthe first reactor of about 2 to 8 moles of hydrogen per mole of hydrocarbon charge stock and introducing additional hydrogen containing gas into the reforming reaction system at a point subsequent to the iirst reaction Zone wherein the volume ratio of paratiin to naphthenic hydrocarbons in the partially converted charge stock is greater than 5:3 in an amount suiiicient to provide an increased ratio of about 10 to 50 ,moles of hydrogen per mole of hydrocarbon charge stock as is described in my copending application Serial No. 136,788, tiled of even Adate herewith now abandoned. Thus, for example, when operating at a recycle ratio of 20 moles of hydrogen per mole of hydrocarbon charge stock, the recycle gas stream passing through line 25 of the drawing is split with about 20 mole percent Abeing introduced into the iirst reactor 4 and the remaining mole percent being introduced into line 11 along with the feed to the third reactor 12, a palladium diffuser being installed in line 11 prior to the point of entry of the recycle gas.

The process of this invention is illustrated in detail in the following examples:

EXAMPLE 1 A fluoride-free platinum-alumina catalyst produced in a commercial plant which manufactures the catalyst of U.S. lPatent 2,808,444 containing approximately 0.6 weight percent platinum in the [form of one-sixteenth inch extrudates in an amount of 20 grams was placed in a one inch inside diameter Universal stainless steel reactor tube dispersed with suiiicient `8 to 14 mesh tabular alumina to provide a catalyst zone of about 250 cubic centimeters volume. The reactor, after each charging, was placed in a bronze-block furnace controlled by thermostats. Bed temperatures were measured by means of platinum and platinum-rhodium thermocouples. Each charge of catalyst was purged with nitrogen gas and then reduced overnight in a slow stream of hydrogen gas at about 900 F. and atmospheric pressure. The mixture of feed and recycle gas passed over the catalyst through the bed and the effluent was passed to a small volume high pressure separator from the top of which a gas phase was taken off for recycle and from the bottom of which a net product con- 8 The operating conditions, yield and product inspection data are shown in the following Table I. Except Where noted, recoveries exceed 97% (most over 98%) and yields are given as the percent on feed and were calculated sisting of condensable liquidplus the net gas production on the basis of 100% recovery. was Withdrawn and introduced into a product stabilizer. Analysis of both gas and liquid samples `for C1 through In order to minimize both holdup and ow upsets inthe C5 hydrocarbons was by gas chromatography. Analysis small volume system, the total net product was contlnuof gas samples for hydrogen was by Orsat. All compoously removed using an air-operated oW control valve nents of a gas sample were determined independently and actuated by a back pressure recordecontroller. The total 10 then summed as a check against errors. A-ll gas analyses net product was fed continuously into a product stabilizer were converted to an air-free basis before use in yield to give a C51' liquid product and a C4 gas. The gas from calculations. the stabilizer was metered and then sampled by diverting The system was pressured with hydrogen and during a portion into an evacuated butyl rubber gas sample bag the sixth to twenty-ninth hours of 4the run, the unit was using a timer actuated solenoid Valve. The recycle gas operated at a recycle ratio of 7:1 and a total pressure was passed through an Ascarite scrubber and dryer for of 350 p.s.i.g. During the hours 29-36, the recycle ratio removal of water and acidic materials such as hydrogen was increased to 55:1 with a consequent drop in product sulde. The Afeed system was a conventional pressure octane. During hours 43-50 and following, methane drop system including an alumina dryer. The feed was analyzing 95.5 mol percent methane and 1.8 mol percent measured volumetrically. The feed and recycle gas dryhydrogen was introduced into the recycle stream and the ers reduced the water content of the total feed to the unit total pressure and recycle ratio were increased so that the to less than 100 parts of water per million parts by volume total amounts of hydrogen in the recycle gas would apof total feed in vapor phase and the Ascarite scrubber proximate those during the initial portion of the run, i.e., substantially completely removed any sulfur from the rchours 6-29. The run demonstrates that the product occycle gas. The unit has proved suitable for accurately tane number remained substantially the same when operdetermining yield-octane relationships. i ating at 600 p.s.i.g. with a high proportion of methane in The `feed charged to the unit was a highly parainic the recycle gas, as when operating normally with a prenaphtha obtained by Udex extraction of a C8 reformate dominantly hydrogen recycle gas at 350 p.s.i.g. During fraction and had the folowing inspections: the initial operations with methane, i.e. during hours 43- 50 the mole percent of hydrogen in the recycle as t. F.: D g 1S ASTl/lsl 4B P 246 estlmated to be approximately 60%. As methane intro- 5% 251 duction continues, however, the mole percent of hydrogen 10% 252 decreases. Thus, to avoid decline in catalyst activity and 20% 254 to achieve the benets of this invention with respect to 30% 256 35 high octane number product at high pressure operation, 40% 258 the mole percent of hydrogen in the recycle gas intro- 260 duced into the reforming system multiplied by the total 262 pressure of the gas so introduced is maintained on the hy- 264 dr0gen-rich side of the methane decomposition equilibl% 269 40 rium but at least about 1% less than the partial pressure 277 of the hydrogen in the hydrogen-containing recycle frac- 286 tion of the eluent from the reaction system. BR 328 The methane decomposition equilibrium varies for Sulfur, pp m 7 4 45 any given set of reaction conditions but can be calculated Density 60/.60 ,716 for a given set of conditions. Higher rates of catalyst Parains, v01. percent 92 deactivation at the methane decomposition equilibrium Naphthenes, v01, percent 0 point, however, indicate operation on the hydrogen excess Aromatics, vol. percent 8 50 side of the methane decomposition equilibrium. The per- Aniline Point, F. 156.6 tinent data appear in the following Table I.

TABLE I [Run N0. 1369] Operating Conditions:

Hours on on, grams 6-13 13-19 19-20I 29-36 43-50 53-61 64-72 72-80 80-88 90-98 98-106 Methane Addition (per grams feed) 25 26 39 38 38 25 27v Temp. F 895.2 895.4 895.5 895.0 885.4 895.1 890.5 895.0 895.6 895.5 895.1 Press., p s 350 350 350 350 600 G00 600 600 600 000 000 HSV.. 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Recycle Ratio.. 7.0 7.0 7.0 55.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Yield Based on 100% Recovery:

Hg, wt. percent 1. 5 1. 3 3.3 4. 0 2. 4 2. 7 2. 1 1. 4 1. 2 01,-(14, wt. preeent 27. 5 16. 9 31.3 3l. 1 25. 9 25. 3 22.3 21. G 21. 4 05+, wt. percent 71.0 81.9 75.7 72.1 77.4 70.0 77.0 77.4. 05+, v01. percent.. 60.4 78.5 09.0 05.0 70.9 70.7 72.0 73.1 C1, Wt. percent.' 2. 3 1. 8 10. 3 10. 3 0. 4 5. 4 1. 0 2. 0 1. 9 C2, Wt. percent- 4. 8 3. 1 6. 8 6. 6 5. 5 5. 5 5. 2 4. 5 4. 2 C3, Wt. percent. 10. 1 6.2 11.8 12.3 10. 4 10. 1 8. 1 7. 4 7. 3 o.. wt. percent. 10.3 5.7 12.7 12.1 10.1 9.7 9.0 7.7 8.3 Aromatics, vol. percent on Feed.. 36 28 37 37 37 38 34 28 30 Product Inspections:

Density, 60/60 0.770 0. 707 0. 768 0. 749 0.781 0.782 0. 790 0. 784 0.778 0. 752 0.700 Annina Point 108.0 110.0 111.0 128.1 110.5 107.8 100.1 111.7 118.4 125.0 125,7 .rngatiea v01. percent 55 52 51 36 53 58 57 53 48 39 42 Ciear 92.8 91.5 90.8 75.1 89.1 91.2 91.0 88.0 83.8 75.7 75.3 +3151 102.4 99.2 99.4 90.3 99.3 99.3 99.0 90.7 94.0 91.1 90.3

, yields cycle cornpiloyed in om the topof d into a palladium diliusion unit -eighth inch outly two feet long. A pressure ressure of the yed in Example phtha having the C, Added 2 Mols/100 g.

Feed) through gas after par-ate pressure gauge bstantially pure hydrogen unit. Substantially bled from the jacketed section at cork RUN 1351 [895 F., 55/1 Recycle] NO C1 EXAMPLE 3 `y the data in this examapparatus was the same as that em 1 except that .the gas phase fr, pressure separator was passe Input Basis Output Basis *Poor recoveries.

Thirdly, even though the octane level is increased re at least as good as without methane.

The effect of hydrogen withdrawal from the re The Example the high diiusion unit prior to recycle. The

'Ihe catalyst was the sarne as that emplo and the feed was a straight run na Hrs. on Ol1 RON Vol. Percent 05+ ple.

side diameter approximate gauge indicated the p leaving the diffusion unit and a se indicated the pressure of the su in the jacketed section of the diffusion pure hydrogen was trolled rates.

following inspections:

250 a 252 253 254 255 256 gas stream is demonstrated b 258 260 263 267 l 277 prrsed a Jacketed palla-drum tube 0f `one 284 302 1.3 .714

TABLE II [Run No. 1351] using a high 9 EXAMPLE 2 The effect of methane addition to the recycle gas on the dehydrocyclization reaction, particularly onstrated by 5' The same apparatus was employed as in Example 1. The catalyst was similar to that of Example 1 except pections were Initial B.P. 5% 10% 20% 30% E.P. Sulfur, ppm. Density 60/60 Aromatics, vol. percent Parafns, vol. percent Aniline Point, F. 156.9

The pertinent data appear in the following Table II 35 l wherein it can be seen from the aromatics content and recycle ratio and a low sulfur feed is dem the data in this example.

that it contained 0.9% by Weight of platinum. The feed was the same as that used in Example 1 exce had been sodium desulfurized. The feed ins as follows:

ASTM Dist. F.:

Sulphur, p.p.rn. Density, F. 0.757 Parains, vol. percent Secondly, catalyst decline rate is not too Naphthenes, vol. percent 75 Aromatics, vol. percent data unambiguously. However, certain facts stand (out. First, addition of methane results in muah higher product octanes than would otherwise be obtained at a given temperature.

greatly increased over that with no addition.

12 in hydrogen production and decrease in methane production.

During hours 140-160, the gas samples Were discarded due to rupture of the diffusion unit. After 215 hours the catalyst was regenerated at 850 F. `and 400 p.s.i.g. using regeneration gas having 0.7% oxygen content.

TABLE III [Run No. 1707] 1 1 The operating conditions, yield and product inspection data lare shown in the following Table III. The data uct octane yas hydrogen is withdrawn from the recycle Also, `the composition ing la, signicant increase show a significant increase in both liquid yield and prodgas stream and the partial pressure of hydrogen in the 5 recycle gas stream is lowered.

of `the make gas is altered show 180 092 4420855518 929 69 660 05 002 28034 217 A115 17 7 7 00 .4 9 .5 3 09 .83. .4 9 .5 83.0. 0.0 m. 4.1.54.A7-O-nwnw N6@ 4 7. LuQUn/u 74 531 306202411 72 29 152 75 531 2706010011 70 0S 14n/a 73 521 2438100621 001 VA 9 188 .0 99 W9 98 .1 99 2 l8r] .9 90 68 01 38 01 m9 0 1 1 1 80 07 082 1721691659 768 36 070 05 062 0846474308 465 7 u 03 .AA 9 5 v 3 u 09 .4 9 .5 M2 74 531 29%@01511 7% 1%2 75 531 27%%01311 7W eo 0.1 %oo 0.1 01540 07 WW2 25.3338022. 4d @2% 14 1 u 1%2. 7.3. .0r/ 1 2.3.4..0m1 2.6.2.l 009m 9.4 9 9 187 0.9 new W. 170 03 081 2630250724 665 87 680 04 O52 2449911124 791 73 5 03 .5 2 .7 .1 04 .5 1 7 52 73 521 2 8224723 84 03 142 73 521 261514622 88 95 2 7H] .8 01 2 187 .8 90 9 0 11 m9 o 1 1 260 02 082 2800887052 927 17 7 09 .5 0 nu 11H2 74 521 2W lo02521 8% Q00 30 06 NM2 570221400z0U M4 88 w70 05 @Q2 244691446.4u we 73 M9 0 1 5.2 7.3. 521 ZmomLQm/ Z uopo. 5.1.. 15.12. 7am 521.. 27.0.41. 1022 conm 0.5. 1 9 1187 .9 90 2 187 .8 90 8 O 1 49 0 0 1 30 09 @mm1 695029891m M500 57 m70 05 mm3 32597881850 U6 55 Uonw 0. meej@ 07. 5.2 7.3. 521 2.&&0.1. 2.5.Lo 87 51 152. 7.3. 521 25.26.15.521 sa 0 5 ...M2 7 5 S2 83 9 187 .9 90 :r2 187 .oo 90 Q Unv 0.9 9m 8 0 1 99 0 1 5 1 170 O2 080 282127110 5 0 6 052 2 5 2 3 09 0. .5 M 06 98. 0. 05 .0.0. ,0. .5.3.0:45 U9. n M2 74 521 2M% 13522 SW km 0.0%2 73 521 2 MMN24622 8% WW 8 0 1 co9 0 11 n 152 7 5 82 84 2 .9 90 wg 0 0 1 1 n 90 00 08 7042072 7 150 0 032 1 02 .3.84 0 .6 o9. @6. 0.7. 06 o .owlljomm 2J 3.5. 42 76 54 171723622 81 9 42 73 521 279414622 86 06 Ov 187 .0 9 12 1h17 .8 00 8 01 80 0 1 1 660 0 0 4 0 NA 5.9. 152 7 5 no2 84 O mw 0.9 9m 9 50 09 00 7401030388 910 08 120 07 072 3165684765 101 45 4 1 02 l .4 9 .6 l 8 06 .5 107 1 02 75 54 162823622 71 39 52 73 521 252713611 89 0 0 69 187 .0 99 42 187 00 8 n 01 70u 0 11 u u u n m. m z e e C f f .1 ...m .m.. 1 \l \/0 tm Em n tm i .nUy m nUy d mUy d uor o uor neV uor l nmw F nmVV F h Bmw F 0 0 v0 t 0 y0 ...u 0 v t .10 n n .16 n U .weO n D m SC O e m StC 0 e m SC 0 e uae C uae C uae c 1 H R ...u r 1 R t I 1 R t r 0 R t n e 0 5R t n e 0 6R t n e s m .1 a n e.. U. s m .1 o n e.. D s m i a n e.. F n ddrV ett tes n ddW .ett tos n ddr ett tos v D 0 1 (eOCnnttttnrn L 0 v (e0tcnnttttnrn FL 0 y (e0tcnntttf urn .M osn. ne0nreennnneeo0Fo .osn. ne0nreennnneeo0 o .1 osn. ne0nreennnneeo0 am mn lbmlmmmmpov .,m efemmlmmmmpov mn aelemlwcmempmv a .l r y a a g1 g. r. x .1 r C I mw Rimmnmwammmwa www@ wr Rrmmnmwrmmmnmww m m0 mmmmnmwtmmmamm. a .ade W DPD. .V 1 .1 ad .a e W .Ppp .V y .1 n a .a 6 D. .ppp .VD y Co etdPt d. l s C0Q- e D d d. .l s a do. d d w. s 1 dov. -oyweet .toten msynwerm: .Vly .imywbet o tw yn. .v: 1m:m3 Co mmv. .mymeem .td .tt -nWemz gs .1 .FITS ...WV CTln gSD. C FS 4 VWWSII g5 C S vvttZLWWSIU mm were. rdmwc ,www :tmm mmmm wrnrndmwc .www -..nimm mNc+ nm wrarnmmwc.. .www ,.wimum .to e v +5+5 .LL4Caom-nr .toe e V. y 1 -4 .Moen rO .U0 o e V. 1 y f4y4toe.m0 a 1 1 u a i 55... 2a C u r 1551,23 Ca r MH R P HmHooooCownmdDAA HTWR P HmHCCooCCwnmdDAAR mH R P HmHCCoooCwnmmDAA o o e 0o e 0o p .1 rr. D. .l fr. D. .l fr 0 Y AP O Y AP o Y AP TABLE III-Continued Operating Conditions: 2

Hurs n Oil. 187-194 194-201 201-208 208-215 /16-12 /12-18 Temp., F 925. 5 925.7 924. 6 925. 0 896. 0 896. 0 WHSV 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 Recycle Ratio, mol/mol:

Total Gas 7.0 7.0 7.0 7.0 7.0 7. 0 Hydrogen. 3.1 3.0 3. 0 3.0 Press., p.s.i.

Total 500 500 499 499 500 500 Hydrogen (diffusion unit).. 220 217 216 212 Hydrogen Bleed Rate, mol/mol ecd 1. 3 1. 3 1. 3 1. 3 Yield Based on 100% Recovery:

H2. Wt. percent 2. 3 2. 3 2. 3 2. 3 1. 7 1.7 (l1-C4, Wt. percent 14. 7 13. 3 13. 2 14. 2 15. 7 14. 5 05+, wt. percent. 83. 0 84. 4 84.5 83. 5 82. 6 83. 8 C54-, vol. percent 77. 2 78. 7 79. 0 78.1 78.7 79. 9 C1, wt. percent. 1. 5 1. 4 1.6 1.8 1. 7 2. 0 C2, Wt. percent.. 3. 6 3. 4 3. 5 3. 5 3. 2 3.0 Ca, Wt. percent." 5.7 5.0 5.1 5.5 5.9 5.1 iCr, Wt. percent." 2. 0 1. 9 1. 9 2. 0 2. 2 1. 9 nCi, Wt. percent 1. 9 1.6 1.1 1. 4 2. 7 2. 5 Aromatics, vol. percent on Feed 54 54 55 54 46 47 Product Inspections:

Density, 60/60- 0. 818 0. 816 0. 814 0.814 0. 799 0.798 Aniline Point, F. 88.9 90.7 90.7 90. 7 101. 1 101. 8 ligatics, vol. percent 70 69 69 69 59 59 ciear 99. 5 99. 5 98. s 9s. s 93. s 93. 2 +3 Uli 104. 8 104. 4 103. 9 103. 9 100. 4 100. 5

EXAMPLE 4 50% 262 60% 264 This example demonstrates the effect of hydrogen With- 70% 266 drawal from the recycle gas stream alone and in com- 80% 270 bination with methane addition to maintain hydrogen 90% 276 content of the recycle gas stream at a given level. 9 5% 283 The apparatus was the same as that employed in EXam- E p 297 ple 3 and the catalyst was the same as that employed in Sulfur, p'pm' 0 4 Example 1- Density 60/60 .722 The feed charged to the unit was a hlghly parainlc Paramus, v01. percent 91 naphtha obtained by Udex extraction of a C8 reformate Naphthenes, VOL percent 0 fraction and had the following inspections: Aromatics VOL percent 9 Aniline Boinlt 68.0 C. ASTM Dist. F.:

Initial B.P. 242 After 212 hours and after the next 25 hours the cata- 5% 252 lyst was regenerated at 850 F. and 400 p.s.i.g. using 10% 254 regeneration gas having 0.7% oxygen content. Recycle 20% 257 ratio was varied from 7 to 55. At hour 42 after the 30% 258 second regeneration, methane was added to the recycle 260 40 gas stream at a point just prior to the reactor.

TABLE IV [Run N o. 1863] Operating Conditions:

Hours on Oil 6-12 12-18 20-26 26-32 32-38 46-54 54-62 62-70 70-78 78- Temp., F 894. 7 894. 7 895. 3 895. l 895. l 895. 3 895. 5 895. 1 895. 1 895. 1 WHS 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 2. 0 Recycle .Ratio 7. 0 7. 0 10. 0 10. 0 9. 9 10.0 10. 1 9. 9 9. 9 l0. 0 Pressure:

Total 500 500 500 500 500 500 500 500 500 500 Hydrogen (diusion unit) 332 332 245 225 215 204 194 192 189 180 Hydrogen Bleed Rate (cn. ft./bbl.

of feed uncorrected) 799 802 802 803 825 803 803 806 Yield Based on 100% Recovery:

H2, Wt. percent 1. 3 1. 3 2. 0 2. 0 2. l 1. 9 1. 9 (l1-C4, Wt. perCenL 27. 6 27. 5 23. 7 24. 4 26. 4 22. 5 20. 8 Cfr, Wt. percent 71. 1 71. 2 74. 3 73. 6 71. 5 75. 6 77. 3 C.5+, Vol. percent 66. 5 66. 8 69. 3 68. 3 67. 3 70. 2 72. 0 C1, wt. percent-.- 3.0 3.0 1. 6 2. 1 2. 0 2.0 1. 71 C2, Wt. percent 4. 2 4. 4 3. 6 3. 9 3. 6 3. 7 3. 4 C3, Wt. percent.-- 10.1 9. 3 7. 9 7.8 6. 9 7. 9 6. 7 i0., wt. percent.. 4. 5 4. 6 4. 6 4. 4 8. 7 4. 1 4. 2 11C., Wt. percent 5.8 6. 2 6.0 6. 2 4. 2 4.8 4. 7 Aromatics, vol. percent on Feed Product Inspections:

Density, /60 0. 7714 0. 7689 0. 7735 0. 7780 0. 7670 0.7770 0. 7750 Aniline Pt., F 42. 2 42. 8 41. 6 41. 6 42. 2 42. 2 42. 6 43. 8 44. 0 44. 6 Armaties, vol. percent 52 51 54 55 53 54 54 51 51 50 R N:

Clear 91. 3 91. 4 92. 6 93. 6 93. 0 90. 6 90. 7 89. 4 89. 1 88. 6 +3 ml 99.3 99.1 99.0 100.1 99.6 99.3 99.3 97. 7 97. 7 97. 1

Operating Conditions:

Hours on Oil 86-94 94-102 102-110 118-126 129-137 143-151 156-161 164-172 172-180 180-188 193-200 Temp. F 895. 1 895. 1 900. 1 905. 4 905. 2 905. 2 905. 0 906. 3 905. 7 925. 2 S 2.0 2.0 2.0 2.0 2.0 2.0 H2.0 2.0) 2.0 2.0 10. 0 10. 0 9. 9 9. 8 10. 2 10. 1 10. 3 10. 3 9. 9 10. 1 Total 500 500 500 500 500 500 500 500 500 500 500 Hydrogen (diffusion unit) 184 179 169 176 165 312 243 188 171 160 297 Hydrogen Bleed Rate (cu. ftjbbl. of feed uncorrected) 801 801 799 782 804 547 764 803 784 234608221 881 87 02 4 8 O .s 3.5 07h/M l 171635945 73 87 52 5 0 1 276 74 89 4 9 N 794458592 00 587081991 W0 8L 74 LOW 99 TABLE IV-Continued 857129347 m 15 0.L L .6.113.845 74 8 77 74 8 nm LLG. .L .6. .5. 65. 7. 27% n0 4 74 8 nw 6. 5. 4 8 n 528 46 198313634 @6.4 7.0 177 n 74 89 Q n n 9 46 ..w rm Y AP erating Conditions:

Hours on Oil Temp., F.- WHSV Recycle Ratio Pressure:

Total. Hydrogen Hydrogen Bleed Rate (cu.

uncorrectcd) Yield Based on Recovery:

H2, wt. pereent 01-04, Wt. percent 05+, wt. percent 05+, vol. percent 01, wt. pereent C2, Wt. pereent Ca, wt. percent.

iCr, Wt. pereent Aromatics, v01. percent er1-Preci Product Inspections:

Density, 60/60 'e'ci' ,"i61'/irli 'a'pt' n04, Wt. pereent Aniline Pt., F

Aromatics, vol. perce Hours on Oil Temp.,

Recycle Rat1o Pressure:

Total-. Hydrogen (diffusion unlt) Hydrogen Bleed Rate (cu. t./bb1. of

uncorrected) Methane Addition R Operating Conditions:

Ha, Wt. percent 01-04, wt. percent.. 05+, wt. percent 05+, vol. percent C1, wt. perceut C2, Wt. pereent C3, wt. pereent iC4, wt. percent 60/60. Aniline Pt., F

n04, Wt. percent Aromatics, vol. percent on Feed Product Inspections:

Densi Aromatics, Vol. pcrcent.

Rate, mol/mol-f-e-ed. Yield Based on 100% Recovery:

wt. percent Operating Conditions:

eed

l. percent on Product Inspections:

*Insufficient sample.

vThe data demonstrate two types of operation: (1) where the hydrogen content of the recycle gas stream is permitted to vary, and (2) where the hydrogen content of the recycle gas stream is maintained substantially constant at a given level permitting optimum operation for a given set of other variables to control product octane and yield and catalyst life.

Examination of the test data in Tables III and IV discloses that significant yield-octane improvement results from the lowering of the hydrogen partial pressure in the reforming of naphthas at a given total pressure. For example, compare normal 500 p.s.i.g. operation at 895 F. with operation at lowered hydrogen partial pressure in the case of a relatively high naphthene content feed.

REFORMING EFFECT OF LOWERED H2 PRESSURE [Run 1707-2 WI-ISV, 7/1 Recycle, 500 p.s.i.g.]

It is seen from the above tabulation that reducing the hydrogen pressure from 428 to 261 p.s.i.g. not only gave a two percent improvement in liquid yield but also a better than two unit improvement in octane level as well. Furthermore, it was possible to improve product octane still more without lowering product yield as, for example, in the 201/208 hour test period. It should also be noted that, after an intervening higher temperature period, a yield improvement of six percent was obtained at the 93 octane level as compared to normal operation (hrs. 65/71 vs. hrs. 12/18).

In addition to the other benefits of operation at low hydrogen partial pressure, hydrogen production is irnproved and methane production is reduced. In normal operation the C2/C1 mol ratio was found to be 1.0` or lower (a value lower than unity indicates excessive methanation). On the other hand, with lowered hydrogen partial pressure operation a ratio as high as 2.4 was obtained (130-136 hrs.). Thus, methane production is inhibited even more than is the total production of light hydrocarbons. There is also an indication that the z'C4/nC., ratio is shifted in a favorable direction.

Lowered hydrogen partial pressure also gave marked improvement in performance with the highly paraftiniclow naphthene content raffinate feed. This is shown by the following data.

REFORMING OF Cs RAFFINATE-EFFECT OF LOWERED Hg PRESSURE [Run 1863-895 F., 2 wsHv, 50o p.s.i.g.]

As in any reforming operation, lowering the relative hydrogen concentration can be expected to result in more rapid catalyst aging. In the case of low hydrogen partial pressure reforming, however, the situation is somewhat more favorable than in normal low pressure operation. This is because the much higher density of the recycle gas makes it possible to use a higher recycle ratio for a given cost than in low total pressure operation. Further, the presence of extra methane in the recycle gas does not contribute -to coke laydown since methane is thermodynamically stable under typical reforming conditions (unlike all other hydrocarbons).

To show what can be accomplished by taking advantage of some of the possibilities of low hydrogen partial pressure operation, a constant temperature, constant octane cycle was programmed with the abnormally high aging rate C8 rafnate feed. Conditions for the run were set at 895 F., 2 WHSV, 55/1 initial gas recycle ratio, and 500 p.s.i.g. total pressure. The -initial two periods of normal operation gave a product of 91-92 octane clear. Thereafter operation was at a reduced hydrogen partial pressure and at an octane level of greater than 91 (clear).

Examination of the third cycle data of Run 1863 (Table IV) show that not only was the rate of catalyst deactivation greatly reduced but that the yields obtained were equal to or better than those of the first cycle. At the 138th hour the recycle ratio was dropped to /1 and at the 189th hour to 20/1. After 206 h-ours of operation the catalyst was regenerated and found to have picked up only 0.7% carbon. On the basis of the third cycle data, it is believed that a cycle life of over 500 hours could be realized at constant octane and constant temperature, with liquid yields equivalent to those of normal 7/1 recycle operation at 350 p.s.i.g.

In lower hydrogen partial pressure operation the hydrogen partial pressure is, of course, a new operating variable. Thus, one can raise both liquid yield and octane level by lowering the hydrogen partial pressure. On the other hand, one can maintain a given hydrogen partial pressure level regardless of catalyst 4aging or changes in other operating variables. Thus in the third cycle of Run 1863, the hydrogen partial pressure was controlled in sequence at three different levels (270, 240 and 185 p.s.i.g.).

A consequence of hydrogen partial pressure control is that it is not necessary to control total pressure in order to control catalyst aging. Thus operation with a floating total pressure is possible with maximum total pressure limited according to safety or other requirements.

Low hydrogen partial pressure operation, as does low total pressure operation, results in greatly increased hydrogen yields. In the case of operation with .a diffusion unit in the recycle gas circuit, as was the situation in Examples 3 and 4, this hydrogen production can be obtained as ultrahigh purity gas and thus is of considerably increased value.

I claim:

ll. In a process for reforming naphtha hydrocarbon stocks in the presence of hydrogen-containing recycle g-as consisting essentially of hydrogen and at least one C1 to C3 alkane with a platinum metal on alumina reforming catalyst in -a reforming reaction system including a successive series of reaction zones under reforming conditions producing a net hydrogen make of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock including temperatures within the range of about 875 to about 990 F., a weight hourly space velocity of 1 to 20, a ratio of about 3 to 50 moles of hydrogen per mole of hydrocarbon charge stock land a total pressure of about 300 to 1000 p.s.i.g., the improvement which comprises separating substantially pure hydrogen from the reforming reaction system at a point intermediate the rst and last reaction zones in an amount of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock.

2. In a process for reforming naphtha hydrocarbon stocks in the presence of hydrogen-containing recycle gas consisting essentially of hydrogen and at least one C1 to C3 alkane with a platinum metal on alumina reforming catalyst in a reforming reaction system including a successive series of reaction Zones under reforming conditions producing a net hydrogen make of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock including temperatures within the range of about 875 to -about 990 F., a weight hourly space velocity of 1 to 20, a ratio of about 3 to 50 moles of hydrogen per mole of hydrocarbon charge stock and a total pressure of about 300 to 1000 p.s.i.g., the improvement which comprises separating substantially pure hydrogen from the reforming reaction system at a point intermediate the first and last reaction zones in an amount of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock by passing the reaction effluent through a palladium diffuser.

3. In a process for reforming naphtha hydrocarbon stocks in the presence of hydrogen-containing recycle gas consisting essentially of hydrogen and at least one C1 to C3 alkane with a platinum metal on alumina reforming catalyst in a reforming reaction system including a successive series of reaction Zones under reforming conditions producing a net hydrogen make of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock including temperatures within the range of about 875 to about 990 F., a Weight hourly space velocity of 1 to 20, a ratio of about 3 to 50 moles of hydrogen per mole of hydrocarbon charge stock and a total pressure of about 300 to 1000 p.s.i.g., the improvement which comprises separating substantially pure hydrogen from the reforming reaction system at a point intermediate the rst and last reaction Zones in an amount of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock up to the net hydrogen make of the reforming reaction system by passing the reaction ellluent through a palla- -diurn diffuser.

4. In a process for reforming naphtha hydrocarbon stocks in the presence of hydrogen-containing recycle gas consisting essentially of hydrogen and at least one C1 to C3 `alkane with a platinum metal on alumina reforming catalyst in a reforming reaction system under reforming conditions including a successive series of reaction zones including temperatures Within the range of about 875 to about 990 F., a Weight hourly space velocity of 1 to 20, a ratio of about 3 to 50 moles of hydrogen per mole of hydrocarbon charge stock and a total pressure of about 300 to 1000 p.s.i.g., the improvement which comprises separating from the reaction eiiluent a gas fraction consisting essentially of hydrogen and at least one C1 to C3 alkane, separating substantially pure hydrogen in an amount of -at least about 250 standard cubic feet per barrel o naphtha hydrocarbon charge stock from at least a portion of the separated fraction, and recycling the fraction so enriched in alkane content to the reforming re-action system by passing the reaction eilluent through a palladium diuser.

5. The process of claim 4 wherein the catalyst is platinum on alumina.

6. In a process for reforming naphtha hydrocarbon stocks in the presence of hydrogen-containing recycle gas consisting essentially of hydrogen and at least one C1 to C3 alkane With a platinum metal on alumina reforming catalyst in a reforming reaction system under reforming conditions producing a net hydrogen make of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock including temperatures within the range of about 875 to about 990 F., a weight hourly space velocity of 1 to 20, a ratio of about 3 to 50 moles of hydrogen per mole of hydrocarbon charge stock and a total pressure of about 300 to 1000 p.s.i.g., the improvement which comprises separating substantially pure hydrogen from the reforming reaction system in an amount of at least about 250 standard cubic feet of hydrogen per barrel of naphtha hydrocarbon charge stock, and adding to the system -a C1 to C3 alkane in an amount suicient to maintain the hydrogen partial pressure in the hydrogen-containing recycle gas Within the range of about to 350 p.s.i.g. and a C1 to C3 partial pressure in said recycle gas higher than about 40% of the hydrogen partial pressure in the hydrogen-containing recycle gas stream.

References Cited by the Examiner UNITED STATES PATENTS 2,550,531 4/1951 Ciapetta 208-138 2,838,444 5/1958 Teter et a1. 208-139 2,863,826 12/1958 Holcomb et al. 208-138 2,870,083 1/1959 Elliott 208-138 2,905,620 9/1959 Haensel 208-138 2,909,480 10/1959 Henke 208-138 2,913,403 l1/l959 Rex et al. 208-138 2,952,611 9/1960 Haxton et al. 208-65 2,984,619 5/1961 Butler et al. 208-65 3,007,862 11/1961 Patton et al. 208-65 DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

H. LEVINE, Assistant Examiner. 

1. IN A PROCESS FOR REFORMING NAPHTHA HYDROCARBON STOCKS IN THE PRESENCE OF HYDROGEN-CONTAINING RECYCLE GAS CONSISTING ESSENTIALLY OF HYDROGEN AND AT LEAST ONE C1 TO C3 ALKANE WITH A PLATINUM METAL ON ALUMINA REFORMING CATALYST IN A REFORMING REACTION SYSTEM INCLUDING A SUCCESSIVE SERIES OF REACTION ZONES UNDER REFORMING CONDITIONS PRODUCING A NET HYDROGEN MAKE OF AT LEAST ABOUT 250 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF NAPHTHA HYDROCARBON CHARGE STOCK INCLUDING TEMPERATURES WITHIN THE RANGE OF ABOUT 875* TO ABOUT 990*F., A WEIGHT HOURLY SPACE VELOCITY OF 1 TO 20, A RATIO OF ABOUT 3 TO 50 MOLES OF HYDROGEN PER MOLE OF HYDROCARBON CHARGE STOCK AND A TOTAL PRESSURE OF ABOUT 300 TO 100 P.S.I.G., THHE IMPROVEMENT WHICH COMPRISES SEPARATING SUBSTANTIALLY PURE HYDROGEN FROM THE REFORMING REACTION SYSTEM AT A POINT INTERMEDIATE THE FIRST AND LAST REACTION ZONES IN AN AMOUNT OF AT LEAST ABOUT 250 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF NAPHTHA HYDROCARBON CHARGE STOCK. 